Heretofore, as a method for producing a reformed gas composed mainly of hydrogen through a reforming reaction by contacting a mixture of a hydrocarbon or an aliphatic alcohol and steam with a catalyst is adopted a steam reforming system wherein heat required for the reforming reaction (endothermic reaction) is given from an exterior through a wall of the reformer as a heat transfer face by means of a combustion burner or the like. In this system, however, for example, when kerosene is steam-reformed, a reforming reaction temperature is required to be about 700-850° C., so that a temperature at the wall of the reformer heated with external heat becomes higher than the reforming reaction temperature, and hence it is necessary to use an expensive material as a material constituting the wall of the reformer. Further, a heating device is required, which has a problem of enlarging the size of the reformer.
To the contrary, there is proposed an autothermal reforming method wherein a mixture of a hydrocarbon or an aliphatic alcohol and steam is further entrained with an oxidizing gas, and a partial oxidation reaction layer is disposed at an upstream side and a steam reforming layer is disposed at a downstream side, and heat generated in the partial oxidation reaction layer of the upstream side is utilized to supplement reforming reaction heat in the steam reforming layer of the downstream side. This method has advantages in which heat loss is small and the reformer can be miniaturized. As a further improved autothermal reforming method are proposed techniques of JP-A-2001-192201, JP-A-2003-335504 and the like.